1. Field of the Invention
The present invention relates to the processing and representation of color images and, more particularly, to a method and apparatus for the representation of color images in data processing systems having monochromatic output devices, such as printers and CRT displays. In this context, an image may be defined as a visual representation of information wherein the information may be pictorial or textual or both and may be comprised of alphanumeric characters or symbols or graphic characters, symbols or elements or a combination thereof. A color image may be further defined as an image wherein the elements or areas comprising the image, whether alphanumeric or graphic, are defined by various colors.
2. Prior Art
Many presently available data processing systems, ranging from public data base television type systems, such as PRESTEL. to `home` computers to very expensive and complex computer aided design (CAD) systems, are capable of manipulating and representing monochromatic and color images. Many systems, however, are wholly or partially limited to monochromatic imagery. either for cost considerations or because image generation and display is a secondary or later added capability of the system. For example, a system may originally have been designed only for monochromatic operations or, while the system itself is capable of operating with color images, the display or hard copy devices connected from the system, such as the CRT and printers, may have only monochromatic capabilities. A recurring problem with systems having image capabilities is presented whenever color images. for example, generated or provided by a system having color image capabilities, are to be visually represented by a system having, for example, only a monochromatic CRT or monochromatic printers. In general, visual outputs of color images by monochromatic means have proven unsatisfactory, the images being esthetically unpleasing or in many cases visually distorted or transformed to an unacceptable extent.
One basis of the problem is that monochromatic and color processes differ in the information presented to a viewer in order for the viewer to distinguish between areas of an image. That is, color processes distinguish between various areas of an image by both color and shade of color, that is, the lightness or darkness of a color. For example, three areas may be distinguished in that one is red, one is light blue and one is dark blue; the red area is distinguished from the blue areas by color and the blue areas are distinguished by being of differing shades of blue. In monochromatic processes, however, the various areas of an image are distinguished only by shade, generally referred to as `half tones`, ranging from `black` to `white`.
A transformation of a color image to a monochromatic image thereby requires that color and shade information contained in a color image be transformed into shade information in a monochromatic image. This results, in present systems, in a loss or distortion of visual information. For example, in the simplest systems the `dark` combinations of color and shade information from a color image are transformed into a `black` monochromatic shade while the `light` combinations are transformed into a `white` monochromatic shade. The result can be a total distortion of the original color image and at least a loss of visual information and a degradation of visual esthetics.
In more complex systems. the various combinations of color and shade appearing in the color image original are transformed into their nearest equivalent `gray scale` monochromatic shade. The most common example of such a system is in `black and white` photography of a colored object, such as a landscape; that is, the various colors and shades appearing in the scene are replaced, in the photograph, by their shade of gray equivalents. While such a system provides less distortion than the simple system described above, there may still be some distortion of the original visual information and often a loss of esthetics. This distortion occurs because many combinations of color and shade have the same `gray scale` equivalent; for example, a red area, a blue area and a green area, easily distinguishable in color, may have the same gray equivalent and appear as the same shade of gray in the monochromatic image.
It is thereby an object of the present invention to provide an improved method and apparatus for representing color images through monochromatic means.